Add support for Snowflake key-pair authentication

[sgrebnov]

Part of #1305

PR adds support for Snowflake key-pair auth via snowflake_auth_type: keypairand snowflake_private_key_path: <path> params. Both unencrypted and encrypted (via passphrase) keys are supported.

version: v1beta1
kind: Spicepod
name: test
datasets:
- from: snowflake:snowflake_sample_data.tpch_sf1.lineitem
  name: lineitem
  params:
    snowflake_auth_type: keypair
    snowflake_private_key_path: /Users/name/rsa_key.p8
    snowflake_private_key_passphrase: 12345

Remaining steps for full key-pair authentication support:

1. Done Add support for encrypted private keys (passphrase/password parameter and logic to decrypt the key)
2. Add key-pair support to Spice CLI (key-pair login for Snowflake)